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Cardiac troponin T (cTnT) is derived from the troponin regulatory complex on the thin filament of the myocardial contractile apparatus. Because the cardiac isoform is distinct from the skeletal muscle isoform9 cTnT specifically identifies myocardial damage in a variety of clinical settings. "0'4 Its cardiac specificity makes it a particularly useful marker for assessing myocardial damage during cardiac surgery'4 by contrast with myoglobin and the MB isoenzyme of creatine kinase that may also be derived from skeletal muscle after cardiac operations."5 A serum cTnT concentration >0 2 ,ug/l detects myocardial injury whereas a value <2-5 jug/l excludes "significant" myocardial injury."3To compare the effects of cold crystalloid cardioplegia and intermittent ischaemic arrest on myocardial preservation 20 patients undergoing coronary artery surgery were randomised to either technique. Efficacy of myocardial protection was assessed by clinical course, electrocardiographic changes, and serial measurements of cTnT. Patients and methods PATIENTSWe studied 20 patients undergoing elective coronary surgery.

In dogs deprived of food and water, water is lost out of proportion to the loss of salt. Concentrations of sodium and of chloride in serum therefore rise progressively for many days, until, just before death, concentrations as high as 186 m.Eq. of sodium and 133 m.Eq. of chloride per liter of serum have been found (1). It was not, however, clear whether death was due to the hypertonicity of the body fluids or to the concomitant dehydration. In certain of the present experiments, a comparable degree of hypertonicity has been produced acutely, without reducing the total body water. In others, hypertonic solutions were administered to animals already dehydrated. The reactions of the animals have been compared with those of the animals in which hypertonicity resulted from water loss alone. MATERIALS AND METHODSTwelve dogs in all were used. Chemical data relating to the fluid and salt exchanges of 8 of them are presented in the preceding paper (2). Two received 5 per cent saline intravenously, the rest intraperitoneally. Four of the animals had their ureters ligated just before the experiment. Dial anesthesia was used in 9 of the acute experiments, morphine in 1 acute experiment, and no anesthetic in the 2 chronic experiments.After the anesthetic had taken effect, the animal was weighed, and a preliminary blood sample and electrocardiogram were obtained. Sodium chloride in 5 per cent solution was then injected intravenously or intraperitoneally. In some experiments, peritoneal fluid was removed after 30 or 40 minutes, in amounts approximating or somewhat exceeding the volume of saline injected.This fluid always contained salt in a concentration much lower than 5 per cent. Serial electrocardiograms were obtained from time to time.

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